Conventionally, in the manufacture of semiconductor devices, micro-processing by lithography using a photoresist has been carried out. The micro-processing is a processing method comprising forming a thin film of a photoresist on a semiconductor substrate such as a silicon wafer or the like, irradiating actinic rays such as ultraviolet rays through a mask pattern on which a pattern for the device is depicted, developing it to obtain a photoresist pattern, and etching the substrate using the photoresist pattern as a protective film. However, in recent progress in high integration of semiconductor devices, there has been a tendency that shorter wavelength actinic rays are being used, i.e., ArF excimer laser beam (wavelength 193 nm) has been taking the place of i-line (wavelength 365 nm) or KrF excimer laser beam (wavelength 248 nm). Along with this change, reflection of exposure light from a substrate have become problems. Accordingly, it has been widely studied to provide an anti-reflective coating (bottom anti-reflective coating) between the photoresist and the substrate.
As the anti-reflective coatings, inorganic anti-reflective coatings made of titanium dioxide, and titanium nitride, etc. and organic anti-reflective coatings made of a light absorbing substance and a polymer compound are known. The former requires an installation such as a vacuum deposition apparatus, a CVD apparatus or a sputtering apparatus, etc. In contrast, the latter is considered advantageous in that it requires no special installation so that many studies have been made. For example, mention may be made of the acrylic resin type anti-reflective coating having a hydroxyl group being a crosslink-forming substituent and a light absorbing group in the same molecule as disclosed in U.S. Pat. No. 5,919,599 and the novolak resin type anti-reflective coating having a hydroxyl group being a crosslink-forming substituent and a light absorbing group in the same molecule as disclosed in U.S. Pat. No. 5,693,691.
The physical properties desired for organic anti-reflective coating include high absorbance to light used for exposure, no intermixing with photoresists (being insoluble in photoresist solvents), no diffusion of low molecular weight compounds from the anti-reflective coating material into the topcoat photoresist, and a higher dry etching rate than the photoresist.
In recent years, miniaturization of process size in a lithography process by use of KrF excimer laser beam or ArF excimer laser beam, that is, miniaturization of formed photoresist pattern size is advanced. In order to prevent collapse or the like of photoresist pattern that is accompanied with miniaturization of photoresist pattern, it is desired to make the photoresist thinner. In addition, when the photoresist is used in a form of thin film, in order to inhibit decrease in film thickness of photoresist layer in the process of removing anti-reflective coating used together by etching, it is desired that the anti-reflective coating can be removed by etching for a shorter time. That is, in order to make the time required for an etching removing step shorter, there are demands for anti-reflective coatings that can be used in a form of thinner film compared with the conventional ones, or for anti-reflective coatings having a higher selection ratio of etching rate to photoresists compared with the conventional one.
It is also requested for the anti-reflective coatings to be able to form a photoresist pattern having a good shape. In particular, it is required to be able to form a photoresist pattern having no footing at the lower part. This is because the photoresist pattern having footing exerts adverse effects on the following processing steps.
In addition, the kinds of photoresists used increase with the progress of lithography technique. Therefore, it is always desired to develop novel anti-reflective coatings in order to adapt to the use of the diverse photoresists.
As an example of such a novel anti-reflective coating, a coating forming composition containing a thiocarbamoyl compound as a light absorbing agent is known (see, for example Patent Document 1). In addition, a base material for a photosensitive resin containing a condensation product of formalin-modified melamine derivative is known (see, for example Patent Document 2). Further, a composition for an anti-reflective coating containing a polymerized aminoplast is known (see, for example Patent Document 3).    Patent Document 1: JP-A-2004-123817 (2004)    Patent Document 2: JP-A-60-220931 (1985)    Patent Document 3: US-B-6323310 (2001)